JPH0651081A - Nuclear reactor stopping device - Google Patents

Abstract

PURPOSE:To quicken the responsiveness for the rise of temp. and insert a control rod certainly in the reactor core. CONSTITUTION:A coil spring 36 is furnished between an upper and a lower extension rod 17, 17 and surrounded by long stretching bellows 34, and a double cylindrical structured thermo-sensitive member 35 is installed outside of the bellows, while a communication hole 31 is formed in the upper rod 17, and a liquid metal 32 is encapsulated in the bellows 34 and the member 35. In this thermal expansion type nuclear reactor stopping device, fins 38 in the form of flat plate are radially installed on the member 35 in the temp. sensing part 29. When the temp. of a cooling material rises in the event of failure in the nuclear reactor, the liquid metal 32 in the thermo-sensitive member 35 rises owing to the fins 38, and the long stretching bellows 34 are displaced by means of passage through the communication hole 31, and the control rod is inserted into the core.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal expansion type reactor shutdown device installed in a fast breeder reactor.

[0002]

2. Description of the Related Art Generally, the core of a fast breeder reactor is composed of a large number of fuel assemblies 1, 1 and a plurality of control rod assemblies inserted between these fuel assemblies 1, 1 as shown in FIGS. Body 2
And a large number of shields (not shown) provided so as to surround the outermost portion of the fuel assembly 1.

The fuel assembly 1 incorporates a large number of fuel pins 3 in a trumpet tube 1a, and an entrance nozzle 4 provided at the lower end of the trumpet tube 1a is inserted into an opening portion of a core support plate 5 so as to be fixed in position. Is installed in.

In the core, a coolant of liquid metal sodium flows from the high pressure plenum 6 in the core support plate 5 into the trumpet pipe 1a through the coolant inlet port 7 of the entrance nozzle 4, and subsequently rises between the fuel pins 3. Then, the fuel assembly 1 is discharged from the handling head above the trumpet tube 1a to remove heat.

The control rod assembly 2 is formed by a lower guide tube 8, an upper guide tube 9, a control rod body 10 and an extension pipe 11 for suspending the control rod body 10. The lower guide tube 8 is installed at a fixed position by inserting the entrance nozzle 12 formed at the lower end into the opening of the core support plate 5.

The entrance nozzle 12 is provided with a coolant inlet 13 communicating with the high pressure plenum 6 and a communication hole 14 communicating with the control rod body 10. Also, the control rod body
A neutron absorber pin is incorporated in the 10.

When the control rod body 10 is reinserted, the control rod body 10
The engaging portion 15 provided at the lower portion of 10 is inserted into the dashpot 16 at the bottom of the lower guide tube 8 and installed at a fixed position. The control rod body (10) has an extension rod (17) extending upward, and a grip portion (18) is formed at the upper end of the extension rod (17). The control rod body 10 is suspended from the extension pipe 11 by grasping the lower end portion of the extension pipe 11 by the grip portion 18.

By vertically moving the extension pipe 11 by a control rod drive mechanism (not shown), the control rod body 10 is inserted into or pulled out from the core. This heat removal of the control rod body 10 is performed by the coolant that rises in the lower guide pipe 8 from the high pressure plenum 6 through the coolant inlet port 13 of the entrance nozzle 12 and the communication hole 14.

As shown in FIG. 12 by enlarging the portion G in FIG. 11, the extension rod 17 is cut, and the coil spring 36 is interposed between the spring portion 30 shown in FIG. 11 and the bellows outside the coil spring 36. A double cylindrical temperature-sensitive member is provided in the temperature-sensing portion 29 shown in FIG. 11 by surrounding the outside of the bellows 34 and the coil spring 36.
35 are provided. Liquid metal sodium is sealed as the liquid metal 32 in the temperature sensitive member 35 and the bellows 34.

Both ends of the bellows 34 are fixed by support plates 33 between the extension rods 17, 17. Both ends of the double cylindrical temperature-sensitive member 35 are sealed with annular end plugs 37. The inside of the bellows 34 and the temperature sensitive member 35 are communicated with each other by a communication hole 31 formed in the extension bar 17 on the upper side.

[0011]

During normal reactor operation, the extension of the extension pipe 11 is adjusted to adjust the insertion degree of the control rod body 10 into the core to adjust the reactor power. Further, when an abnormality such as an abnormal increase in the reactor output or a decrease in the coolant occurs, a scram operation is carried out to urgently insert the control rod body 10 into the core and stop the furnace.

On the other hand, in a fast breeder reactor, it is assumed that the extension pipe 11 cannot be lowered for some reason in an emergency and the control rod body 10 cannot be inserted into the core. It is necessary to keep the reactivity below the critical level.

The reason for this is that if a scrum failure occurs, the reactor power will increase excessively and the temperature of the coolant will rise, which may lead to a core damage accident.

FIG. 13 shows the relationship between the reactivity and the accident time. As shown in FIG. 13, when the scram fails, the criticality of the control rod reactivity is 0 due to the Doppler effect and the coolant density effect in the core. A higher positive reactivity of the line a in FIG.

However, in the conventional thermal expansion type reactor shutdown device, the extension pipe 11 and the extension rod 17 expand axially as the temperature of the coolant increases due to an accident, and the control rod body 10 is inserted into the core. However, the reactivity indicated by the line b in the figure occurs.

Conventionally, the total reactivity obtained by superimposing these positive and negative reactivities is kept in the negative positive reactivity region lower than the critical level as shown by the line c in the figure, and the safety of the nuclear reactor is improved. Have secured.

In the conventional thermal expansion reactor shutdown device, the liquid metal in the temperature sensing member thermally expands in response to the temperature rise of the coolant caused by the scrum failure at the time of abnormal reactor operation. However, there is a problem that it takes time until the temperature of the liquid metal in the temperature sensitive member is raised, and the negative reactivity effect due to the expansion of the control rod cannot be sufficiently promptly obtained.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a reactor shutdown device which has excellent responsiveness to a rise in temperature of a coolant and which can surely insert a control rod into a core. .

[0019]

According to the present invention, there is provided a control rod body housed in a guide tube installed in a reactor core so as to be able to move up and down, an extension rod extending upward from an upper end of the control rod body, and an extension thereof. An extension pipe that engages with a grip portion provided on the upper part of the rod to suspend the control rod body, a spring interposed in a part of the extension rod, a bellows that interlocks with expansion and contraction of the spring, and the bellows and A double-cylindrical temperature-sensing member surrounding the outside of the spring, a liquid metal sealed in the temperature-sensing member and the bellows, and a communication between the bellows and the temperature-sensing member. In the reactor shutdown device including the communication hole, a fin is attached to the temperature-sensitive member or the temperature-sensitive member is formed in a corrugated shape to increase a heat transfer area. Further, it is characterized in that liquid lithium is used as the liquid metal, or a fuel pin is provided in an annular shape around the control rod body.

[0020]

When the fin is attached to the temperature sensitive member, the fin quickly transfers the heat of the coolant due to the liquid metal in the bellows. Therefore, the temperature rise time of the liquid metal in the temperature sensitive member is shortened, and the thermal expansion of the liquid metal in the temperature sensitive member is accelerated. Therefore, the negative reactivity effect due to the expansion of the control rod is immediately obtained.

Further, by making the temperature sensitive member wavy and increasing the area of the heat transfer surface, the temperature rise of the coolant can be more quickly transferred to the liquid metal in the bellows. Therefore, the temperature rise time of the liquid metal in the temperature sensitive member is shortened, the thermal expansion of the liquid metal in the temperature sensitive portion is accelerated, and the negative reactivity effect due to the expansion of the control rod is immediately obtained.

Furthermore, by using liquid lithium as the liquid metal in the bellows, the Li (n, α) reaction of lithium in the bellows is accompanied by an increase in the neutron flux level when the reactor power is excessively increased. Fever increases. Therefore, the temperature rise time of the liquid metal in the temperature sensitive member is shortened, and the thermal expansion of the liquid metal in the temperature sensitive portion is accelerated. Therefore, the negative reactivity effect due to the expansion of the control rod is immediately obtained.

Further, by providing the fuel pin in an annular shape around the main body of the control rod, the output of the fuel pin increases when the reactor is abnormal. Along with this, the temperature of the coolant around the fuel pin rises, and this raised coolant directly reaches the temperature sensitive member. Therefore, the temperature rise time of the liquid metal in the temperature sensitive member is shortened, and the thermal expansion of the liquid metal in the temperature sensitive portion is accelerated. Therefore, the negative reactivity effect due to the control rod expansion is immediately obtained.

[0024]

【Example】

(First Embodiment) A first embodiment of the reactor shutdown device according to the present invention will be described with reference to FIGS. Note that FIG.
2 is an enlarged vertical sectional view of the portion A in FIG. 1, and FIG.
It is a sectional view taken along arrow B. 11, those parts which are the same as those corresponding parts in FIGS. 11 and 12 are designated by the same reference numerals, and a description of the overlapping parts will be omitted.

FIG. 1 shows that the first embodiment is different from the conventional example.
The fins 38 having a flat plate shape are radially attached to the temperature sensing portion 29 shown in FIG. Other configurations are similar to those of the conventional example.

That is, the temperature sensitive portion 29 shown in FIG. 1 comprises a double cylindrical temperature sensitive member 35 as shown in an enlarged view in FIG. Thus, the flat fins 38 are radially attached to increase the heat transfer area.

Next, the function and effect of the first embodiment having the above structure will be described. When the temperature of the coolant rises when the reactor is abnormal, the fins 38 protruding into the coolant quickly transfer the temperature rise of the coolant to the liquid metal 32 in the temperature sensitive member 35. Therefore, the liquid metal 32 in the temperature-sensitive member 35 expands while the temperature rises, passes through the communication hole 31, and reaches the bellows portion.
Displace 28 long bellows 34 and insert the control rod into the core.

As a result, the control rod body 10 is inserted into the core more quickly than in the conventional case, so that in the event of an abnormality in the reactor, the negative reactivity effect due to the expansion of the control rod can be immediately obtained. (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. 5 is an enlarged vertical sectional view showing a portion C of FIG. 4, and FIG. 6 is a sectional view taken along the line D-D of FIG. 11, those parts which are the same as those corresponding parts in FIGS. 11 and 12 are designated by the same reference numerals, and a description of the overlapping parts will be omitted.

The difference of the second embodiment from the conventional example is that the outer tube of the temperature sensing member 35 of the temperature sensing portion 29 is formed in a wavy shape as shown in an enlarged view in FIG. Has been increased. In addition, a reinforcing rod to reinforce the strength of the temperature sensitive part 29.
39 is attached to the extension rod 17 and the temperature sensing unit 29, and a reinforcing ring 40 is installed so as to bundle the reinforcing rods 39.

Next, the function and effect of the second embodiment will be described.
When the temperature of the coolant rises when the reactor is abnormal, the area of the heat transfer surface of the temperature sensing unit 29 is large, so that the temperature rise of the coolant is quickly transferred to the liquid metal 32 in the temperature sensing member 35. Therefore, the liquid metal 32 in the temperature sensitive member 35 expands as the temperature rises, passes through the communication hole 31, displaces the bellows 34, and inserts the control rod into the core.

As a result, the control rod body 10 is inserted into the core more quickly than in the conventional case, so that in the event of an abnormality in the reactor, the negative reactivity effect due to the expansion of the control rod is immediately obtained.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 8 shows E of FIG.
It is a longitudinal cross-sectional view which expands and shows a part. Figure, Figure 11 and Figure
The same parts as 12 are designated by the same reference numerals, and the description of the overlapping parts will be omitted.

The third embodiment is different from the conventional example in that the liquid metal in the temperature sensitive member 35 and the bellows 34 is replaced with the conventional liquid sodium by the liquid lithium 41.
The other configurations are the same as those of the conventional example of FIG.

Next, the function and effect of the third embodiment will be described.
When the reactor power is abnormally increased and the neutron flux level is increased when the reactor power is excessively increased, the Li (n, α) reaction by the liquid lithium 41 in the temperature sensitive member 35 and the bellows 34 is increased. An increase in heat generation due to the Li (n, α) reaction instantaneously occurs. For this reason, the time during which the temperature of the liquid lithium 41 of the temperature sensitive member 35 is raised is shortened, and the thermal expansion of the liquid metal in the temperature sensitive member 35 becomes rapid. Therefore, the displacement of the bellows 34 becomes quick, and the time for inserting the control rod into the core becomes short.

As a result, the control rod main body 10 is inserted into the core more quickly than in the conventional case, so that when an abnormal state occurs in the reactor, the negative reactivity effect due to the expansion of the control rod can be immediately obtained. (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 10 shows a cross-sectional view taken along the line FF of FIG. 9, and more particularly, a cross-sectional view inside the lower guide tube 8 between the fuel assemblies 1 and 1. In the figure, the same parts as those in FIGS. 11 and 12 are designated by the same reference numerals, and the description of the overlapping parts will be omitted.

In this embodiment, a fuel pin 42 is provided in an annular shape around the control rod body 10 inside the lower guide tube 8 between the fuel assemblies 1 and 1. The opening area of the communication hole 14 is widened in order to secure the coolant flow rate of the fuel pin 42. In addition, the previously installed introduction pipe has been deleted.

Next, the function and effect of the fourth embodiment will be described.
When the reactor is abnormal, the output of the fuel pin 42 inside the lower guide pipe 8 rises, and the temperature of the coolant around the fuel pin rises accordingly. The temperature-increasing coolant is directly connected to the temperature sensitive member 35.
Reach Therefore, the time during which the temperature of the liquid metal 32 of the temperature sensing unit 29 is raised is shortened. The liquid metal 32 of the temperature sensing section 29 expands while the temperature rises, passes through the communication hole 31, displaces the bellows 34, and inserts the control rod into the core.

As a result, the control rod main body 10 is inserted into the core more quickly than in the conventional case, so that when an abnormal state occurs in the reactor, the negative reactivity effect due to the expansion of the control rod can be immediately obtained.

[0039]

According to the present invention, since the temperature rise of the coolant at the time of reactor abnormality is utilized, the responsiveness to the ambient temperature rise is quick and the control rods are more reliably transferred into the core. It can be inserted and can give a large negative control rod reactivity to the core. Therefore, even if a scrum failure accident occurs, the reactor power can be automatically attenuated, and the inherent safety of the reactor can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first embodiment of a reactor shutdown device according to the present invention.

FIG. 2 is a vertical cross-sectional view showing an enlarged part A in FIG.

FIG. 3 is a transverse cross-sectional view taken along the line BB in FIG.

FIG. 4 is a longitudinal sectional view showing a second embodiment of the reactor shutdown device according to the present invention.

5 is a vertical cross-sectional view showing an enlarged part C in FIG.

FIG. 6 is a transverse cross-sectional view taken along the line D-D in FIG.

FIG. 7 is a vertical cross-sectional view showing a third embodiment of the reactor shutdown device according to the present invention.

FIG. 8 is a vertical cross-sectional view showing an enlarged part E in FIG.

FIG. 9 is a vertical cross-sectional view showing a fourth embodiment of a nuclear reactor shutdown device according to the present invention.

FIG. 10 is a transverse cross-sectional view taken along the line FF in FIG.

FIG. 11 is a vertical sectional view showing a conventional reactor shutdown device.

12 is an enlarged vertical cross-sectional view showing a G portion in FIG.

13 is a characteristic diagram showing the relationship between the reactivity and the accident time in FIG.

[Explanation of symbols]

1 ... Fuel assembly, 2 ... Control rod assembly, 3 ... Fuel pin, 4
... Entrance nozzle, 5 ... Core support plate, 6 ... High pressure plenum, 7 ... Coolant inlet, 8 ... Lower guide tube, 9 ... Upper guide tube, 10 ... Control rod body, 11 ... Extension tube, 12 ... Entrance nozzle, 13 ... Coolant inlet, 14 ... Communication hole, 15 ... Engagement part,
16 ... Dash pot, 17 ... Extension rod, 18 ... Gripping part, 28 ... Bellows part, 29 ... Temperature sensing part, 30 ... Spring part, 31 ... Communication hole, 32 ...
Liquid metal, 33 ... Support plate, 34 ... Long bellows, 35 ... Temperature sensitive member, 36 ... Coil spring, 37 ... End plug, 38 ... Fin, 39 ... Reinforcing rod, 40 ... Reinforcing ring, 41 ... Liquid lithium, 42 … Fuel pin.

Claims (2)

[Claims] 1. A control rod body housed in a guide tube installed in a core so as to be able to move up and down, an extension rod extending upward from an upper end of the control rod body, and a grip provided on an upper portion of the extension rod. An extension pipe that engages with a portion to suspend the control rod body, a spring interposed in a part of the extension rod, a bellows that interlocks with the expansion and contraction of the spring, and surrounds the bellows and the outside of the spring. A double cylindrical temperature-sensitive member provided as a liquid metal enclosed in the temperature-sensitive member and the bellows,
A communication hole that communicates the inside of the bellows and the inside of the temperature-sensitive member, and a fin is attached to the temperature-sensitive member, or the temperature-sensitive member is formed in a corrugated shape to increase a heat transfer area. A reactor shutdown device characterized in that 2. A control rod body housed in a guide tube installed in the core so as to be able to move up and down, an extension rod extending upward from the upper end of the control rod body, and a grip provided on the upper portion of the extension rod. An extension pipe that engages with a portion to suspend the control rod body, a spring interposed in a part of the extension rod, a bellows that interlocks with the expansion and contraction of the spring, and surrounds the bellows and the outside of the spring. And a double cylindrical temperature-sensitive member, a liquid metal sealed in the temperature-sensitive member and the bellows, and a communication hole communicating between the bellows and the temperature-sensitive member. A nuclear reactor shutdown device characterized in that liquid lithium is used as the liquid metal, or an annular fuel pin is provided around the control rod body.